This invention relates to electrical scales having a load receiver and means associated with said load receiver for furnishing a plurality of counting pulses varying in number as a function of the weight of said load. The scale further has apparatus for summing the counting pulses over predetermined time intervals and a digital display for displaying the sum.
Several types of scales are included, such as, for example:
Scales with electromagnetic load compensation in which a current which is proportional to the weight is digitalized and displayed in units of weight. Such scales are for example described in U.S. Pat. Nos. 3,688,854 and 3,786,884.
Scales with mechanical oscillators, for example strings, whose frequency changes as a function of the weight of the applied load. The change in frequency constitutes the digital representation of the weight. Such a scale is described, for example in U.S. Pat. No. 3,897,681.
A number of mutually contradictory requirements must be considered when specifying the predetermined time intervals for summing up the counting pulses (integration time). On the one hand the accuracy of the indication and the resolution of same are to be as high as possible, which requires a relatively long integration time with correspondingly large number of digits in the display. On the other hand, the relatively long time required for such a measurement is not desirable and, where only a rough indication of the weight is desired, quite unnecessary. Thus scales with different integration times have already been suggested. In these, a manual activation of a switch allows switching from long integration times with high display resolution for exact weighings, to short integration times with a relatively low resolution for correspondingly less exact weighings and vice versa (U.S. Pat. Nos. 3,786,884 and 3,788,411). Among other difficulties, these known solutions have the drawback that the additional manual operation during weighing is too inconvenient to be competitive in today's market.
In U.S. Pat. No. 3,826,319, the possibility of varying the number of digits in the display as a function of the amount of undesired movement of the scale is indicated. This known arrangement has the disadvantage that the integration time remains the same throughout and is therefore no solution to the present problem.
U.S. Pat. No. 3,789,937 discloses a scale in which control means are provided to prevent a display of the weight while the moveable part of the scale is undergoing excessively large oscillations about its equilibrium position, and no display is furnished during the transient condition.